একটি আলোর তরঙ্গদৈর্ঘ্য 6000Å। এর শক্তি কত?

$\begin{aligned} \lambda & =6000 \AA=6 \times 10^{-7} \mathrm{~m} \\ E & =\frac{h c}{\lambda}=\frac{\left(6.63 \times 10^{-34}\right) \times\left(3 \times 10^{8}\right)}{6 \times 10^{-7}}\end{aligned}$

$\begin{aligned}= & 3.315 \times 10^{-19} \mathrm{~J} \\ & =\frac{3.315 \times 10^{-19}}{1.6 \times 10^{-19}} \mathrm{eV} \\ \therefore E & =2.07 \mathrm{eV}\end{aligned}$